This invention relates, generally, to the field of electronic data transmission, and more particularly to the transmission of data over a radio frequency channel such as that utilized by a cellular telephone link.
Recently, the availability of cellular telephone communication service has increased dramatically. All major metropolitan areas, and many less populated areas, are served by at least one cellular telephone company. The development of this cellular network has resulted in providing a widespread capability to communicate with a mobile telephone subscriber by the use of an RF cellular telephone channel and the existing public switched telephone network, almost anywhere in the country. As cellular telephone systems and equipment have proliferated, there has developed an increased demand for the transmission of not only voice information, but also data. Unfortunately, the transmission of data over a cellular telephone link presents additional problems not encountered with the transmission of simple analog voice information.
In particular, while the introduction of noise into voice communication may create some problems of intelligibility, in general, unless there is a complete loss of signal, the voice message will still be transmitted and recognized. On the other hand, when transmitting data in a digital form, any noise encountered on the communications channel will most likely corrupt the data being transmitted, thereby requiring the same data to be retransmitted. Similarly, a break in transmission while transmitting data, as is often the case in cellular transmissions, requires retransmission of all of the data. Retransmission of data results in a lower throughput bandwidth due to the extended time necessary to transmit data. In addition, since the cellular network is more expensive to use due to its associated higher tariffs (compared to comparable land lines), such retransmission can increase operating costs substantially.
While it has been known to interface common data terminal equipment and modems to a cellular telephone transceiver, such attempts have not been optimized for use in a cellular RF environment, and thus are large, expensive and inefficient.
Accordingly, it has been determined that the need exists for an improved apparatus for the transmission of data over an RF channel which will provide increased reliability of data transmission as well as a reduction of operating costs, thereby improving upon the above-noted limitations of the prior art.
Accordingly, it is an object of the invention to provide an improved apparatus for the transmission of data over an RF channel.
It is another object of the invention to provide an improved apparatus for the transmission of data over an RF channel where the channel is a cellular telephone link.
It is a further object of the invention to provide an improved apparatus for the transmission of data over an RF channel whereby a connection will not be attempted until the signal level of the data channel is above a predefined threshold.
It is still a further object of the invention to provide an improved apparatus for the transmission of data over an RF channel wherein the communication link will be automatically disconnected when it has been determined that the signal level has fallen below a predetermined level.
It is yet another object of the invention to provide an improved apparatus for the transmission of data over an RF channel wherein the standard Microcom(copyright) network protocol (MNP(copyright)) (defined hereinafter) is modified so that all transmitted packets are continually repeated until the remote modem acknowledges receipt or is disconnected by an auto disconnect mechanism.
It is still another object of the invention to provide an improved apparatus for the transmission of data over an RF channel whereby, when a communications link is dropped due to poor signal quality, the connection will be transparently re-established and the session will be continued from the point where the disconnect interrupted the transmission.
It is yet a further object of the invention to provide an improved apparatus for the transmission of data over an RF channel which tracks the costs associated with the use of a cellular telephone channel.
It is even another object of the invention to provide an improved apparatus for the transmission of data over an RF channel which is optimized to reduce the costs associated with the transmission of data over a cellular telephone channel.
It is yet an additional object of the invention to provide an improved apparatus for the transmission of data over an RF channel which may be integrated to an existing cellular telephone transceiver.
It is even another object of the invention to provide an improved apparatus for the transmission of data over an RF channel to improve upon the limitations noted in the prior art.
Still other objects and advantages of the invention will, in part, be obvious and, will, in part, be apparent from the specification.
Generally speaking, in accordance with the invention, an apparatus for the improved transmission of data over an RF channel is provided. The invention, which optimizes the transmission of data through a cellular network, provides an effective mobile data solution which increases data throughput while also lowering user costs.
In a preferred configuration, the invention is designed to monitor a cellular channel""s signal strength and only permit communications when the signal level is above a. predefined threshold, from which it may then be determined that a call reliably can be made.
In addition, the invention embodies an automatic disconnect on low signal strength so that should a call be initiated in an area where the signal strength is sufficient to permit reliable data communications, but the data channel quality then becomes degraded during transmission, communications will automatically be halted in order to reduce the number of unsuccessful retransmission attempts, and thereby reduce unnecessary associated telephone costs.
The invention further incorporates a modification to the Microcom Network Protocol (MNP), a protocol designed and developed by Microcom, Inc. of Norwood, Mass., and described at length in Microcom Network Protocol Specification Link Services Class 1-4, October, 1987 and Microcom Network Protocol Specification Class 10, Version 1.0, October, 1991, whereby transmitted packets of data are continually repeated until the remote modem acknowledges receipt of the packet or is disconnected by the above-described auto disconnect feature.
Further to the development of the invention is an automatic dial connection restoration mechanism whereby, when a communications link is dropped due to noisy or poor quality transmission conditions, the connection between the transmitting and receiving stations will be transparently re-established and the transmission of data will resume from the point of the last known good packet transmission, thereby reducing the costs associated with the retransmission of the entire file.
Finally, the invention also incorporates billing timers which may be used to supplant the normal billing information which is available over a standard wired telephone system, but which is not provided with a cellular telephone system.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangements of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.